1. Field of the Invention
The present invention relates to a system and method for relaying Multicast Broadcast Service (MBS). More particularly, the present invention relates to a system and method for relaying MBS employing an Adaptive Modulation and Coding (AMC) scheme.
2. Description of the Related Art
Recently, studies on MBS capable of providing broadcast services more efficiently for mobile WiMAX are under progress.
MBS is an efficient mechanism to transmit same data to all users participating in the MBS using shared system resources. MBS technique is defined by IEEE802.16e standards, so detailed description on it will not be provided in this specification.
MBS zone, which is a group of base stations (BS) serving synchronized MBS contents data to mobile stations, provides MBS data with the single frequency network operation scheme. It is also obvious to people skilled in the art that multiple MBS zones are also feasible.
Mobile WiMAX system can transmit data to a target mobile station using a 16-bit connection ID (CID) in MAC layer. It also supports macro diversity, which improves the probability of successful data reception and reduces power consumption and overall interference.
Despite the features described above, the performance of MBS system is easily influenced by location and mobility of mobile stations, channel condition, etc. To increase the performance of MBS, therefore, an efficient modulation and coding scheme is required.
In downlink mode, Mobile WiMAX system uses three types of modulation: Quadrature Phase Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (QAM), and 64 QAM. The modulation scheme, combined with the coding scheme, is used as Modulation and Coding Scheme (MCS) levels. With suitable modification of the MCS levels, it becomes possible to achieve high data throughput and keep a specific Bit Error Ratio (BER).
Although Mobile WiMAX system with higher MCS level may have higher throughput, it does not necessarily guarantee stable services due to its sensitivity to channel conditions.